Decreased contraction to phenylephrine by ouabain in 2K-1C rat aorta is modulated by the endothelium

The effects of ouabain were studied on the contraction stimulated with phenylephrine or KCl in intact endothelium and denuded aortic rings isolated from normotensive (2K) and renal hypertensive 2 kidney-1clip (2K-1C) rats. Ouabain did not change the basal tone of aortic rings. Ouabain (1 nmol/l) had no effect on the contraction to phenylephrine in all the artery groups studied. Ouabain (10 nmol/l) decreased the Emax to phenylephrine in intact endothelium arteries from 2K-1C. By contrast, ouabain (10 nmol/l) had no effect on the contraction to KCl. Ouabain induced membrane depolarization measured by confocal image with Di-4-ANEPPS dye, that was greater in 2K than in 2K-1C rat aorta smooth muscle cells. In conclusion, ouabain (10 nmol/l) decreased the contractile responses to phenylephrine only in 2K-1C rat aortic rings with intact endothelium. Interestingly, 10 nmol/l ouabain depolarizes the smooth muscle cells but this depolarization level is not enough to alter the phenylephrine or KCl-induced contractions. Our results indicate that the endothelium modulates the vascular action of ouabain.